The Linguistics skill covers all of the uses of the 3.5 skills Forgery and Decipher Script. The Linguistics skill also covers the ground of the old Speak Language skill; you gain languages based on the amount of ranks you have in the Linguistics skill. Normally you gain one language per rank, but there are some exceptions, as listed below. The following are the languages from my setting(s).
Terrasan: This is the official language of the Terrasan Empire (surprising, I know) and as such is widely spoken in all the areas of the map shown on my campaign sites and elsewhere. In origin, it is based on the southern shores of the Mezzovian Sea, and it is there that its penetration is most thorough. That said, since no land shown on the map has failed to undergo a fairly severe "Terrasification" culturally, this is a common trade language, at least, if not native language of most people in the area.
Real life similarities: Most place and people names here come from this language. To represent this, I've used mostly Occitan and Catalan names and words, with a few that I draw or manually revise from Romanian, Spanish and various Italian and other Romance languages as well, such as Sardinian, Asturian, Aragonese, Piedmontese, Corsican, Sicilian, etc.
North Terrassan (Balshatoi): The Terrasan Empire was cobbled together over the course of many generations, and from many cultures. The northern rim of the Mezzovian Sea was originally populated by a completely different cultural group. Due to the many years that they have been part of the Empire, their language had largely faded, to be used only by lower classes (particularly, isolated rural populations) and scholars who read the ancient records of the region. As the strength of the Empire has faded in recent decades, however, North Terrassan has undergone a bit of a linguistic renaissance. More and more people of the northern cities: Razina, Iclezza and their surrounding lands, are trying to reclaim the language and bring about its greater prominence. This effort is still nascent; a person who speaks only Terrassan and not North Terrassan will get along fine in these cities, although more and more certain officials, merchants and others will view them as worthy of scorn or even resentment for attempting to "stamp out" their own native culture. Despite the name, North Terrassan is related to Terrassan only by way of geography. Linguistically the languages bear little resemblances that aren't obvious recent borrowings.
Real life similarities: Names in North Terrassan can be picked from Scandinavian and Slavic namelists, particularly Old Norse and Polish or Russian.
Common: Common in this setting is not like Common in a typical D&D setting. Common is a patois or Creole type language formed from Terrassan and various other substrate languages, and it has never achieved anything like a legitimate status. Although a few people write glosses and other short passages in various alphabets, especially Terrassan, this is merely an accomodation; Common actually has no written form at all. Speaking in Common is certainly possible over a wider audience than Terrassan, but it is limited in what it can convey; it lacks the robustness of a naturally occuring language.
Roleplaying note: Realistically, anyone roleplaying in this setting can use Common to get by (although there is no written form of it) without any penalties. For added flavor, anyone trying to conduct any social skill check (Diplomacy, Bluff, Intimidate, etc.) in Common takes a -2 penalty due to the simplistic and sparse nature of speaking in Common.
Kvuustu: Kvuustu is a language that originates in the southern portion of the map, and is most closely associated with the orc population. It's too simplistic to simply say that Kvuustu is the equivalent of the orc language, however; many humans who live in proximity to that area speak Kvuustu as their native language as well. Many scholars believe that this language was once much more widespread over this area, long before the rise of the Terrassan Empire, and that ironically it was humans from the shores of the Mezzovian Sea who first brought an ancient form of this language to the orcs... who now bring it back with their foederati army legions and settlements. Many orcs who are recently arrived in the Empire speak only this language, or at best, Kvuustu and Common. Kvuustu does have an ancient written form, but today few people can use it and most native speakers are illiterate.
Real life similarities: I actually have a word generator program, with custom parameters, that generate my Kvuustu words. It is notorious amongst Terrassans for its difficult consonent clusters and long "doubled" vowels, as well as having fewer phonemes than some other languages. In fact, the more difficult consonent clusters compensate for this lack of phonemes, so that k-, kv-, ksv-, etc. serve as different letters from each other, effectively.
Kurushi: The language of the Kurushat khaganate, this language is commonly known by its association with the hobgoblins, who speak it as a native language. Unlike Kvuustu, this language is quite cultured, and the hobgoblins themselves can claim to have a growing, vibrant, powerful state that is a legitimate rival to Terrasa and other states in the region. In any case, Kurishi has a rich literary history, at the very least, and its use, especially on the southern rim of the Mezzovian, is fairly commonplace.
Real life similarities: If the Terrassan empire is often compared loosely to Rome, then the Kurushi have to be compared loosely to the Sassanian Persians, at least in terms of role in the setting, if not actual linguistic similarity. The fact that the goblins who remain here are isolated from their motherland, and have been for a long time, does not mean that they have forgotten their heritage. Although many serve as foederati for Terrassa, their primary allegiance is to themselves. The names I've created for Kurushat are often Leigh Brackett Martian names that have been modified and malformed to scrape the serial numbers off. In addition, a pseudo-Asian vibe has been applied to some names, although this is too vague and generic to be binned to any specific Asian culture.
Sylvan: This language comes from the woods and wilderness areas on the western borders of the Empire, and is still common amongst the rural mining towns in Caurs Mountains and the woodlands of the southern Bisbal Forest especially along the banks of the Erau River. Because many Imperial citizens only know it from the shifters who live in that region, it is informally called "Shifter" or Vucari by many. Another branch of this language exists deep in the Shifting Forest, but since the inhabitants of those lands are extremely xenophobic and don't maintain relationships of any kind (other than "kill on sight") with their neighbors, this dialect has diverged from that spoken in the Caurs region significantly.
Real life similarities: Most Sylvan names are ones that I've grabbed from namelists from Georgian (the country, not the state in the southeastern United States) and Turkish. I might have grabbed a few Abhkhaz names just for fun as well.
Qizmiri: This language came from across the ocean with the jann. The version of Qizmiri today is heavily influenced by a substrate language of the humans who lived there, who spoke a language distantly related to Terrasan. That language is now extinct, and everyone from Qizmir speaks Qizmiri.
Real life similarities: Most names and words from Qizmiri are borrowed and adapted from either Farsi or Arabic, and should have a similar "feel" to those languages.
Tarushan: Tarushan is mostly a substrate language of the northern reaches of the map, distantly related to North Terrasan. It's mostly extinct except as a source of ancient inscriptions, placenames and loanwords. However, it does remain an active and vibrant language in one region: Tarush Noptii. It is speculated that it is the original native language of the Primogenitor vampires. The linguistic conservatism of effectively immortal creatures has ensured that it remains mostly as it was many generations ago, and today Tarushan is one of the most archaic and conservative languages in the region.
Real life similarities: Tarushan names are borrowed from Hungarian.
Infernal: This is the primary language spoken by those from the Realms Outside, although myriad other tongues exist amongst this diverse breed as well. In addition, this is the language of magic, so a smattering of it, at least, is known by any practitioner of the arcane arts. Perfect fluency in this language, on the other hand, is almost impossible for any mortal to achieve. Because of this, it takes two skill points to earn this language, not one.
Despite that, it was always very fashionable in Baal Hamazi, where the demonic taint of their bloodline was a source of pride to the ruling caste, to speak Infernal natively, and many noble houses took great pains to ensure that their children didn't hear any other language until they were five years of age. Some households still speak Infernal in the home, and it is still a living language of some importance in some of the successor states to Baal Hamazi, and amongst the hamazin in particular.
Dagonic: This is a bizarre pre-human language, remnants of which float around on isolated and moldy standing stones and other areas. Intriguingly, it appears to have originally been a underwater language. Few people on the surface can even make an attempt to learn it, due to the challenges of speech that an underwater language had to have overcome, and the language itself is only known from very scanty and fragmentary remains, making fluency all but impossible for even the most dedicated scholar.Roleplaying note: Because of the difficulty in learning this language, it takes three skill points rather than one to do so. Also, for all intents and purposes, it is a written language only, not a spoken language, since there are no speakers that anyone knows of at all, and how to pronounce the language is anyone's guess.